Medical instruments, etc. conventionally used in medical sites each have an alarm device because the actions and the like of the instrument are involved in the life of each patient. For example, when it is necessary to supply blood to a patient during an operation, etc., a medical instrument such as an extracorporeal circulator that has an artificial heart-lung apparatus or the like for circulating the patient's blood extracorporeally, and such an extracorporeal circulator is also provided with an alarm device (see, for example, Japanese patent publication JP2006-325750). In a case of the extracorporeal circulator, which circulates the patient's blood extracorporeally, the extracorporeal circulator is configured so that the alarm device operates and outputs an alarm signal when, for example, an abnormality in a flow rate or the like of the circulating blood or an abnormality in pressure or the like has been detected.